Method of treating cementitious objects



Patented Aug. 1, 1944 Calvin Arthur Owens, Los Angeles, Calif.

No Drawing. Application May 20, 1941, Serial No. 394,363

7 Claims. (Cl. 117-123) This invention pertains to methods of treatingcementitious bodies and objects for the purpose of increasing thewater-tightness and impermeability of such bodies and for the purpose ofPreventing, retarding or ameliorating eiilorescence, surface checking,cracking or crazing. Generally stated, the invention pertains to atreatment of cementitious bodies and objects (generally made from ahydraulic cement composition) with a solution containing'a reagenthereinafter; described in greater detail.

This application is a continuation-in-part of a co-pending applicationSerial No. 260,743 filed March 9, 1939, entitled Treatment of hydrauliccement compositions."

Hydraulic cements, generally known as Portjects made from or composed inlarge part at least, of hydraulic cement or hydraulic cementcompositions. For example, the present invention is applicable-tothetreatment of cement pipe or tanks made from cementitiouscompositions, whether such pipe or tanks have been made from the usualhydraulic cement composipreviously compositions with the inventiondetions or from cement treated in accordance scribed in the parentapplication for Letters Patent.

Generally stated, the present invention .is

based upon the discovery that by making a water land cements, contain anumber of silicates and aluminates, some of which involve calcium, thisbeing generally referred to as lime. Part of this calcium or lime iscombined with the silica, alumina and other components, in relatively.stable form, while another part may lyzable or in the form of oxide,hydroxide or carbonate, these rather reactive and readily hydrolyzableportions being the source of what is termed free or available lime. Thepermeability of hydraulic cement compositions and their susceptibilitytothe action of water are believed to be due, in part at least, to thepresence of free lime or soluble constituents which are readily leachedout of the cementitious bodies, resulting in a porous mass which can bedisruptedreadily by ice formation, growth of salt and sulfate crystalsin such pores, etc.

Furthermore, porosityor permeability of the compositions permits thewater to gain access to whatever steel, iron or other metal is containedwithin or covered by the hydraulic cement composition, the moisture,together with its contained salts, forming an electrolyte which ac-.

celerates and renders possible corrosion of such steel, iron or othermetal. The corrosion in turn results in the formation of oxides and anincrease in volume which causes spalling and further exposure of themetals.

In the parent application for Letters Patent above noted (of which thisis a continuation-inpart) the preparation of hydraulic cementcompositions in such manner that the resulting cemntitious the passageof water and other liquids has been described. This application isprimarily directed to the treatment of previously formed objects. suchas for example, existing walls, roads, foundations, roofs, pipe andother structures or obbodies are relatively impervious to.

be readily hydro- I solution of certain metallic compounds, such aswater solutions of compounds of chromium, molybdenum, tungsten orvanadium, and applying such solutions to previously formed hydrauliccement surfaces and objects, such objects may be rendered much moreimpervious to the passage of water therethrough than prior to suchtreatment. An object of this invention, therefore, is to disclose. andprovide a method of converting relatively soluble constituents ofhydraulic cement or cementitious compositions into relatively insolublecompounds which are retained within the compositions or bodies and whichretard subsequent penetration of such bodies by other solutions. Otherobjects, advantages, characteristics, uses and adaptations of theinvention will be made evident to those skilled in the art from thedescription given herein.

In accordance with the present invention the treating agent to be usedcomprises a solution containing a water-soluble compound of chromium,molybdenum, tungsten or vanadium, or any mixture thereof. Compoundsemployed should not be strongly basic nor strongly acidic and should notgive rise to the formation of calcium compounds having large molecularvolume upon crystallization with water, such as calcium sulfate, forexample. Chromic anhydride, manganese trioxide, molybdic acid andammonium salts of molybdenum, vanadium and tungsten are examples ofmaterials which can be employed. Chromic anhydride is preferred. Chromicanhydride is often referred to as chromic acid, but ir respective of thename used, it is desirable that the substance employed in this processbe able to dissolve in water to furnish, in part at least, the ionswhich are furnished by the addition of CrO: to water. It is believedthat chromic an- CraOio and CnOia tioned being the most common.Technical grades of chromic anhydride can be used.

Aqueous solutions of desired compounds from the group given hereinabovemay be made either in final strength form or in concentrated form andthen diluted for use in the field. Solutions containing from 1% to 20%or even more (say 30%) of chromic acid may be used in washing, spraying,swabbing, saturating or impregnating previously cast, poured orotherwise formed hydraulic cement compositions.

Floor slabs, tank walls, retaining walls, dams, and objects such asbowls, plugs, conduits and the like, may have their permeability to thepassage of water greatly decreased by flooding r washing the surfaces ofsuch masses or by spraying or dipping such bodies with or into a watersolution of mineralizing reagent of the character hereinabove stated,such as chromium anhydride. Such treatment apparently results in the.formation of calcium chromate and relatively insoluble chromiumcompounds, such as chromium hydroxide, within the porosities of thepreviously formed hydraulic cement masses; the relatively insolublemetallic compounds thus formed having a tendency to fill up previouslyexisting voids and thereby increasing the resistance of the object ofstructure to the subsequent penetration of water thereinto. Thetreatment is particularly adapted to the use of objects which havev notbeen surfaced or finished.

After the object has been swabbed, impregnated or otherwise treated withthe solution in accordance with the present invention, it is desirablethat such object be permitted to thoroughly dry before being placed intoservice, many of the compounds formed becoming highly insoluble afterthey have been dried even though the originally formed compounds,together with their combined water, are somewhat soluble. Largestructures such as dams may be treated by drilling into such structuresand pumping the solutions thereinto under pressure.

The treatment herein disclosed is not limited to objects made fromhydraulic cement compositions and consisting of only hydraulic cementand sand or other aggregation; the treatment is also applicable toobjects made from compositions containing any appreciable amount ofhydraulic cement. For example, composition shingles containing only 15%to 20% of hydraulic cement and a high proportion of other ingredients,such as asbestos fiber, may be rendered highly moisture resistant bybeing treated with a 15% solution of chromic acid. I

- In someinstances, it may be desirable to carry out the impregnationunder vacuum conditions.

cement compositions That is, the object to be impregnated may be placedinto a closed receptacle, the air evacuated from such receptacle and asolution then admitted into the receptacle so as to completely fill theporosities. Thereafter the suction may be discontinued and thereceptacle opened so as to permit the object to be withdrawn from thesolution.

Those skilled in the art will appreciate from the above description thatnumerous changes, modifications and adaptations can be made in the useof the invention and that all changes and adaptations coming within thescope of the following claims are embraced thereby.

I claim:

1. A method of reducing the permeability of hydraulic cement bodieswhich comprises: treating the surface of such bodies with a watersolution of chromic anhydride.

2. A method of increasing the strength and water resistance of objectsmade from hydraulic cement compositions which comprises: treating suchobjects with an aqueous solution containing a water-soluble reagent fromthe group consisting of chromic anhydride, manganese trioxide, andmolybdic acid.

3. A method of increasing the strength and water resistance of objectsmade from hydraulic which comprises: treating such objects with anaqueous solution containing a water-soluble reagent from the groupconsisting of chromic anhydride, manganese trioxide, and molybdic acidand then permitting the objects to dry.

4-. A method of increasing the water resistance of objects made fromhydraulic cement compositions which comprises: wetting the objects withan aqueous solution containing from about 5% to 25% by weight of chromicacid.

5. A method of increasing the water resistance of objects made fromhydraulic cement compositions which comprises: wetting the objects withan aqueous solution containing from about 5% to 25% by weight of chromicacid and then drying such objects.

6. A method of increasing the water resistance objects made fromhydraulic cement compositions which comprises: impregnating the objectswith an aqueous solution containing from about 5% to 25% by weight ofchromic acid.

7. A method of increasing the water resistance of objects made fromhydraulic cement compositions which comprises: impregnating the objectswith an aqueous solution containing from about 5% to 25% by weight ofchromic acid and then drying such objects.

CALVIN ARTHUR OWENS.

